Separator systems are used in industry for a variety of undertakings. They are used to process dry materials and liquid/solid slurries. Each one typically functions by first introducing a flow of material to a porous element such as a screen or filter, usually of woven wire mesh or a porous membrane. The flow of material is separated into two streams, one containing material that passes through the porous element, the other containing material that is rejected by the porous element. A drive mechanism may be operatively coupled with a housing to produce a vibrating motion that serves to put the material on the porous element in motion until it either passes through or is pushed off the element at the periphery thereof. Other devices use pressure to increase flow through a membrane with cycled application including reverse flow to clear the rejected material.
Such separator systems employ screens in rectangular and circular forms with screen elements tensioned on frames or with hooks tensioned on the separator itself. The screen elements range greatly in porosity and can be of a single element or of laminated elements. The separator frames can be vibratory or fixed and, when vibratory, supported by a variety of means such as springs, bushings or links. Such systems alternatively employ filters, tensioned or untensioned, supported or unsupported and of widely varying porosities and shapes including rectangular, circular, cylindrical and bag shaped. Many additional features are, of course, available such as housing covers, elaborate manifolds and various and changeable motions, rates and cycles. Patents disclosing a small sampling of such systems and components include U.S. Pat. No. 4,022,693; U.S. Pat. No. 4,251,354; U.S. Pat. No. 4,582,597; U.S. Pat. No. 4,613,432; U.S. Pat. No. 4,655,911; U.S. Pat. No. 4,968,366; U.S. Pat. No. 5,032,210; U.S. Pat. No. 5,051,171; U.S. Pat. No. 5,134,893; U.S. Pat. No. 5,221,008; U.S. Pat. No. 5,226,546; U.S. Pat. No. 5,242,058; U.S. Pat. No. 5,255,789; U.S. Pat. No. 5,265,730; U.S. Pat. No. 5,271,504; U.S. Pat. No. 5,456,365; U.S. Pat. No. 5,950,841; U.S. Pat. No. 6,089,380; U.S. Pat. No. 6,202,856; U.S. Pat. No. 6,349,834; U.S. Pat. No. 6,431,368; and U.S. Pat. No. 6,513,665, the disclosures of which are incorporated herein by reference.
Materials typically screened vary considerably in their particle size, bulk density, chemical composition, temperature, moisture content and other physical and chemical characteristics. Any particular separator system in a given processing plant is likely dedicated to handling a single material with consistent properties. Examples of such materials, to show the diversity but not to provide a comprehensive list, include:
abrasives, activated carbon, calcium carbonates, ceramic slurries, chlorine compounds, citric acid, fertilizers, flours, food products, gunpowder, minerals, paper coating slurries, pharmaceuticals, pigments, polystyrene beads, powdered metals, powdered paints, printing inks, PVC powder, refractories, rocket propellants, and starches.
As a result, various screen configurations, vibration profiles and environments are employed to maximize efficiency and the quality of the resulting processed materials.
By far the most common failure mode for separator systems is the failure of the porous element. Screens, for example, are typically made of finely woven wire cloth drawn taut by a screen frame or tensioning apparatus on the separator. Failure is caused by numerous factors such as wear and fatigue failure. Such failures typically occur as breaks in the screening media itself resulting in a damaged screen. Such breaks may manifest themselves as tears (a series of mutually adjacent broken wires), punctures (tears in two directions) or holes (missing portions of the screening material). Once the screen has failed, the function of a separating system is compromised. At a minimum, it can no longer be relied upon to reject all oversized material because such material can now pass through the break in the screen. Worse, it can result in fragments of the failed screen contaminating the material being screened, presenting a serious hazard in food or pharmaceutical screening operations. Similar failure occurs in filter elements.
A system to detect breaks in porous elements has been developed using RF signals. Such a system is described in pending U.S. patent application Ser. No. 10/668,114 filed on Sep. 22, 2003 incorporated herein by reference. A signal system is employed with a vibratory material separator to define a separator system. The signal system includes a signal transmitter and a signal receiver located to either side of a screen in the separator. The signal system and the components thereof operate in the RF (radio frequency) range and, more practically given the size of the preconfigured interstices of commercial screens, operate in the higher end of the RF range in the microwave range, with the signal system, the transmitter and the receiver being microwave elements. The signals are understood to fall in the range of 700 megaHz to 50 gigaHz with specific empirical tuning to match the characteristics of the screen employed.
The signal source recognizes a change in a physical state of the screen when a break occurs through the received RF signal to the receiver and generates a signal as may be desired by the operator, to sound an alarm, to open the power switch to the separator, etc.
Gaskets are typically used at the interface of a screen frame and vibratory separator housing members. The gaskets used are usually made from an RF transmissible material, thereby permitting RF signals to pass through the gasket. Further, the thickness of the gasket separates the conductive components of the housing and screen frame by a distance sufficient for an RF signal to be transmitted through the gasket between the conductive, RF shielding, components. Thus a signal, typically indicative of a break in the porous element, may be detected by the receiver although the porous element remains intact. It is therefore desirable to provide an RF shield between the screen frame and the housing components of the vibratory separator to prevent such false detection. When pharmaceuticals and food are to be processed by the vibratory separator, the material from which the gasket used to seal the screen and the housing is made may have to meet certain requirements. Typically, the portion of the gasket that potentially comes into contact with the pharmaceuticals or food being processed is preferred to be made from a white elastomer. As the processing of food and pharmaceuticals is often more heavily regulated and implements more stringent requirements than other industries, it would be an improvement in the art to have a gasket that can shield RF signals while meeting requirements and regulations for food processing equipment.